论文标题
使用带有内部标记的示踪剂颗粒直接测量涡度
Direct measurement of vorticity using tracer particles with internal markers
论文作者
论文摘要
当前的涡度测量实验技术具有有限的空间和时间分辨率，以解决湍流中的小规模涡流动力学。在这项研究中，我们开发了一种基于数字Inline全息图（DIH）的流体流中直接涡度测量的新方法。 DIH系统利用准直的激光束用内部标记和数字传感器照亮示踪剂，以记录产生的全息图。使用标准的微流体液滴发生器制造由聚二甲基硅氧烷（PDMS）与内部标记混合的示踪剂。根据3D位置重建和内部标记的跟踪开发了旋转测量算法，并通过合成全息图评估，以识别最佳参数设置和测量范围（例如，在0.25的数值孔径下，旋转速率从0.3到0.7 RAD/帧的旋转速率）。我们提出的基于DIH的方法是通过单示踪剂旋转的校准实验评估的，该实验得出相同的最佳测量范围。使用vonKármán旋转流程设置，我们进一步证明了该方法同时测量多个示踪剂的拉格朗日旋转和翻译的能力。我们的方法可以在小区域中以100 $ $ m或更少的速度测量涡度，并且可以潜在地用于量化湍流中的Kolmogorov尺度涡度场。
Current experiment techniques for vorticity measurement suffer from limited spatial and temporal resolution to resolve the small-scale eddy dynamics in turbulence. In this study, we develop a new method for direct vorticity measurement in fluid flows based on digital inline holography (DIH). The DIH system utilizes a collimated laser beam to illuminate the tracers with internal markers and a digital sensor to record the generated holograms. The tracers made of the polydimethylsiloxane (PDMS) prepolymer mixed with internal markers are fabricated using a standard microfluidic droplet generator. A rotation measurement algorithm is developed based on the 3D location reconstruction and tracking of the internal markers and is assessed through synthetic holograms to identify the optimal parameter settings and measurement range (e.g., rotation rate from 0.3 to 0.7 rad/frame under numerical aperture of imaging of 0.25). Our proposed method based on DIH is evaluated by a calibration experiment of single tracer rotation, which yields the same optimal measurement range. Using von Kármán swirling flow setup, we further demonstrate the capability of the approach to simultaneously measure the Lagrangian rotation and translation of multiple tracers. Our method can measure vorticity in a small region on the order of 100 $μ$m or less and can be potentially used to quantify the Kolmogorov-scale vorticity field in turbulent flows.
